1. Field
The present invention is concerned with novel fluoro-substituted phenyl-cyclohexylacetylenes, their preparation, liquid crystalline mixtures containing such compounds and the use of these compounds and mixtures for electro-optical purposes.
2. Description
Liquid crystals are used primarily as dielectrics in indicating devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices employing liquid crystals are well-known and can be based on various effects. Such devices include, for example, dynamic scattering cells, DAP cells ("deformation of aligned phases"), guest/host cells, TN cells ("twisted nematic structure"), STN cells ("super twisted nematic"), SBE cells ("super birefringence effect") and OMI cells ("optical mode interference"). For displays having a high density of information, actively controlled cells, such as TFT ("thin film transistor") cells have recently become an important addition to passively controlled multiplexed cells. However, most common indicator devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.
Liquid crystal materials should have good chemical, photochemical and thermal stability, in addition to good stability towards electric fields. Further, these materials should have a suitable mesophase over a range which is as broad as possible (for example, a nematic or a cholesteric phase for the aforementioned cells) as well as sufficiently high viscosity. When used in cells, liquid crystal materials should permit short response times, low threshold potentials and high contrast. Further properties such as the electrical conductivity, dielectric anisotropy and optical anisotropy should fulfill requirements depending on the field of application and type of cell. For example, materials for cells having a twisted nematic structure should have maximal dielectric anisotropy and minimal conductivity, the latter property being particular important for TFT cells. Components having high dielectric anisotropy and low conductivity are in demand.
Such compounds are provided by the present invention.